There are two broad classes of fuel gases, based not on their chemical composition, but their source and the way they are produced: those found naturally, and those manufactured from other materials.
Manufactured fuel gas Manufactured fuel gases are those produced by chemical transformations of solids, liquids, or other gases. When obtained from solids, the conversion is referred to as
gasification and the facility is known as a
gasworks. Manufactured fuel gases include: •
Coal gas, obtained from pyrolysis of coal •
Water gas, largely obsolete, obtained by passing steam over hot
coke •
Producer gas, largely obsolete, obtained by passing steam and air over hot
coke •
Syngas, major current technology, obtained mainly from
natural gas •
Wood gas, obtained mainly from
wood, once was popular and of relevance to
biofuels •
Biogas, obtained from landfills •
Blast furnace gas •
Hydrogen from
Electrolysis or
Steam reforming The coal gas made by the pyrolysis of coal contains impurities such a tar,
ammonia and
hydrogen sulfide. These must be removed and a substantial amount of plant may be required to do this.
Well or mine extracted fuel gases In the 20th century,
natural gas, composed primarily of
methane, became the dominant source of fuel gas, as instead of having to be manufactured in various processes, it could be extracted from deposits in the earth. Natural gas may be combined with hydrogen to form a mixture known as
HCNG. Additional fuel gases obtained from natural gas or
petroleum: •
Propane •
Butane • Regasified
liquefied petroleum gas The composition of natural gas varies widely, but the table shows a typical composition. Natural gas is produced with water and gas condensate. These liquids have to be removed before the gas can be used as fuel. Even after treatment the gas will be saturated and liable to condense as liquid in the pipework. This can be reduced by superheating the fuel gas. == Specification ==